lookup_dcookie - return a directory entry's path

Look up the full path of the directory entry specified by the value cookie. The cookie is an opaque identifier uniquely identifying a particular directory entry. The buffer given is filled in with the full path of the directory entry. For lookup_dcookie() to return successfully, the kernel must still hold a cookie reference to the directory entry.

EFAULT The buffer was not valid. EINVAL The kernel has no registered cookie/directory entry mappings at the time of lookup, or the cookie does not refer to a valid directory entry. ENAMETOOLONG The name could not fit in the buffer. ENOMEM The kernel could not allocate memory for the temporary buffer holding the path. EPERM The process does not have the capability CAP_SYS_ADMIN required to look up cookie values. ERANGE The buffer was not large enough to hold the path of the directory entry.

Linux 2.5.43. The ENAMETOOLONG error was added in Linux 2.5.70.

Standard C library (libc, -lc)

lookup_dcookie - return a directory entry's path

lookup_dcookie() is a special-purpose system call, currently used only by the oprofile(1) profiler. It relies on a kernel driver to register cookies for directory entries. The path returned may be suffixed by the string " (deleted)" if the directory entry has been removed.

On success, lookup_dcookie() returns the length of the path string copied into the buffer. On error, -1 is returned, and errno is set to indicate the error.

oprofile(1) Linux man-pages 6.9.1 2024-05-02 lookup_dcookie(2)

Linux.

#include<sys/syscall.h> /* Definition of SYS_* constants */ #include<unistd.h>intsyscall(SYS_lookup_dcookie,uint64_tcookie,char*buffer,size_tlen);Note: glibc provides no wrapper for lookup_dcookie(), necessitating the use of syscall(2).